1. Field of the Invention
This invention relates to a successive plane type color camera which uses a rotatable color filter and a single image pickup device to successively output video signals of primary colors R, G and B, and in particular to a successive plane type color camera endowed with the registration correcting function which eliminates color misregistration during reproduction.
2. Related Background Art
A successive plane type color camera is such that as shown in FIG. 6 of the accompanying drawings, a rotatable filter 2 installed in front of the image pickup surface of an image pickup device 1 such as an image pickup tube or a solid state image pickup element is rotated, whereby video signals of three primary colors, i.e., red, green and blue (hereinafter referred to as "R, G and B") are output successively. That is, video signals of R, G and B are successively output from the image pickup device 1, as shown in FIG. 7 of the accompanying drawings. FIG. 7 is simplified as by omitting the horizontal retrace line period of scanning.
Now, in the successive plane type color camera, image pickup is effected by the single image pickup device 1 and therefore, the color misregistration when a color picture plane is reproduced on the basis of the video signals of three primary color does not exist in principle and registration correction for preventing color misregistration is not necessary.
However, the fact that the angle of mounting of the rotatable filter 2 is not perpendicular to a rotary shaft and the non-uniformity of the thickness (t) of the material forming the rotatable filter 2 may cause the occurrence of color misregistration.
FIGS. 8A, 8B and 8C of the accompanying drawings show, with time, the manner in which the filter 2 is rotated when the video signals of the primary colors R, G and B in a case where the rotatable filter 2 is not mounted perpendicularly to the rotary shaft, and as shown there, the distance between the rotatable filter 2 and the image pickup surface and the relative angle between the rotatable filter 2 and the image pickup surface differ when the video signals of the primary colors R, G and B are introduced, and as a result, color misregistration occurs.
FIG. 9 of the accompanying drawings shows the course of a light ray transmitted through a rotatable filter 2 having different thicknesses ta and tb. This course can be primarily found from the refractive indices of air and the material forming the rotatable filter 2.
Light emitted from one end and the same light source A is image-picked up at different points B and B' because of the different thicknesses ta and tb of the material forming the rotatable filter 2 and as a result, color misregistration occurs.
Thus, even the successive plane type color camera in which color misregistration does not occur in principle has actually suffered from the problem that color misregistration occurs.